One of the most important problems in designing microwave devices is suppression of undesired modes. Their presence in the spectrum of the output RF signal impairs the device characteristics, namely, reduce the operational stability range, decrease its efficiency and gain factor, etc.
At present, to enhance the stability of the operating frequency (operating frequency range), use is made of generating or amplifying microwave devices with means for suppressing undesired modes.
There is known a microwave device (cf. U.S. Pat. No. 3,221,204; Nov. 30, 1965) comprising cavities and additional chambers with microwave absorbers.
The internal dimensions of the chambers are selected such that their operating frequency range is not covered by that of the microwave device.
Also known is a microwave device (cf. U.S. Pat. No. 3,221,205; Nov. 30, 1965) comprising a cathode which emits electrons into the space defined by the cathode and cells of an electrodynamic or anode system. The cells are connected in parallel with individual filters via coupling elements, the filters being electrically associated with microwave absorbers to suppress undesired modes.
The filters in this prior art device are different constructions of transmission line (waveguides, coaxial cables, periodic loaded waveguides).
However, the use of such filters does not provide for simultaneous suppression of the undesired modes on either side of the operating frequency or operating frequency range of the device. Besides, the filters introduce attenuation within the operating frequency range, which results in a lower efficiency of the circuit and the device as a whole.